A reference conversation is worth an hour and most people spend fifteen minutes on it, asking questions that cannot produce a useful answer.
Who to ask for
A client with a team the size yours will be, in a comparable kind of role, engaged for at least eighteen months. Each of those matters: a two-person team tells you nothing about running twenty, a developer team tells you nothing about bookkeeping, and anything under a year has not been through a departure yet.
Ask for two. The second is always less prepared than the first.
Three questions that work
What went wrong in the first three months? Something did. The answer tells you what the provider's onboarding is weak at and whether they fixed it.
What would you do differently? Almost always answered honestly, and almost always about the client's own preparation rather than the provider, which is itself the most useful thing a prospective client can hear.
What does this provider do badly? Every long relationship has an answer. A reference with none has been selected for enthusiasm rather than for information.
Two more if the conversation is going well
How many people have you been through in this role, and why did the previous ones leave? Attrition described from the client's side is more informative than a percentage.
How much of your own time does it take now, compared with what you expected? This calibrates the number in the entry on real cost against somebody who has lived it.
What not to ask
Whether they are happy. The answer is yes, it is unfalsifiable, and it consumes the goodwill you need for the useful questions.
Checking the reference is a reference
Look the business up. A referee at a company with a shared director, a shared address or an obvious commercial relationship with the provider is not independent, and this is checkable in a few minutes.
It is uncommon and it happens, and the check costs nothing.
References you can find yourself
Former staff. Employer review sites for this industry are active in this country and the reviews describe the employer rather than the service, which is a different and useful angle: a provider staff dislike will have the attrition you were asking about.
Read the volume and the pattern rather than individual reviews. Anonymous reviews skew negative everywhere and a consistent theme across many is worth more than any single account.
The site visit
If the engagement is large enough to justify the airfare, go. An hour in the office tells you about the equipment, the density of desks, the noise, whether the supervisors are present, and whether the place looks like somewhere people stay.
Announce it rather than arriving unannounced. An unannounced visit produces a worse conversation and no better information, and it starts the relationship as an inspection.
What a reference cannot tell you
Whether the provider will suit you. It tells you how they behaved with somebody else, whose preparation, management and roles were different from yours.
The predictive value of references generally is modest, which is the honest position, and they remain worth doing because the failure modes they surface are specific and checkable rather than general.
Writing down what you heard
Immediately, in a shared note, including the parts that were lukewarm. Reference conversations blur within a week and the lukewarm parts are the ones that turn out to have been the warning.
The reference nobody asks for
A former client. Providers will not volunteer one and some will supply one if asked, and a business that left tells you more about how a relationship ends than any current client can.
A refusal is not damning. The willingness to have the conversation is informative either way.
How long the conversation should be
Half an hour, booked, with the questions sent ahead. A referee given a proper meeting answers properly; one caught on a call gives you adjectives.
Offer to return the favour. Most people asked to be a reference for a provider are happy to, and most have never been asked the three questions above.
What to do with a mixed reference
Most useful ones are mixed. A referee who describes two real problems and says they would engage again has given you a picture; one who describes none has given you a testimonial.
Take the two problems to the provider and ask what changed. The answer to that is worth more than the reference was.